Satellite communication systems are used in a variety of applications, ranging from television broadcast to Internet access. For example, the Digital Video Broadcasting (DVB) consortium specifies a transmission system for hybrid satellite and terrestrial digital television broadcasting to mobile terminals in a standard entitled “Framing Structure, Channel Coding and Modulation for Satellite Services to Handheld Devices (SH) below 3 GHz,” DVB Document A111 Revision 1, Jul., 2007, which is incorporated herein by reference. This standard is referred to as DVB-SH. Other digital video broadcasting standards can be found at www.dvb.org.
Satellite communication channels are typically characterized by deep fades and signal blockage periods, particularly in urban areas. Several methods and systems for reducing the effects of fading and signal blockage are known in the art. Some of these methods employ Error Correction Coding (ECC) and time interleaving. For example, section 5.4.3 of the DVB-SH standard, cited above, describes an exemplary time interleaver configuration.
An exemplary communication method for the Land Mobile Satellite (LMS) channel is described by Ernst et al., in “Transport Layer Coding for the Land Mobile Satellite Channel,” Proceedings of the 2004 59th IEEE Vehicular Technology Conference (VTC-2004), Milan, Italy, May 17-19, 2004, volume 5, pages 2916-2920, which is incorporated herein by reference. The paper describes a method, which uses an additional layer of coding at the transport layer and spreads the sent packets over time, so as to create an extremely long virtual interleaver. The paper further investigates the use of Low-Density Parity Check (LDPC) codes.
As another example, Eberlein et al., describe an exemplary Forward Error Correction (FEC) scheme for mobile reception of satellite signals in “Double Use of the Link Margin—Advanced Physical Layer for Satellite Broadcast to Mobile Users,” Proceedings of the 2005 Joint Conference: 11th Ka and Broadband Communications Conference and 23rd International Communications Satellite Systems Conference, Rome, Italy, Sep. 25-28, 2005, which is incorporated herein by reference. The paper further describes an air interface that uses very long time interleavers.
Various interleaving schemes for mobile satellite applications are described by Eberlein et al., in “Comparison of Physical Layer Interleaving with Upper Layer Interleaving,” Proceedings of the Seventh Workshop on Digital Broadcasting, Erlangen, Germany, Sep. 14-15, 2006, which is incorporated herein by reference.
Some video transmission methods, commonly known as Scalable Video Coding (SVC), transmit a composite signal, which comprises multiple components having different quality levels, e.g., different compression depths. The different components are encoded at different levels of ECC or other protection means. A terminal receiving the composite SVC signal decodes the signal components that match its channel conditions and/or computational capabilities. Some aspects of SVC operation are described, for example, by Wu et al., in “Scalable Video Coding and Transport over Broadband Wireless Networks,” Proceedings of the IEEE, Volume 89, Issue 1, January, 2001, pages 6-20, which is incorporated herein by reference. Another SVC application is described by Schierl et al., in “Wireless Broadcasting using the Scalable Extension of H. 264/AVC,” IEEE International Conference on Multimedia and Expo (ICME-2005), Amsterdam, The Netherlands, Jul. 6-8, 2005, pages 884-887, which is incorporated herein by reference.